PNS Flashcards
(31 cards)
What does the muscle spindle consist of and what do each of them do?
2 intrafusal fibres – Nuclear bag and nuclear chain.
Nuclear bag - muscle length and velocity (dynamic)
Nuclear chain - muscle length (tonic)
What does the gamma and alpha motor neuron do in the muscle spindle
Gamma – activates the muscle spindle (contractile ends of spindle fiber); making it shorter or longer changes the spindles sensitivity
Alpha – innovates extrafusal fibres and activates the muscle contraction via regular skeletal muscle fibres
What are the 4 types of info conveyed by sensory system?
Modality
Location
intensity
Timing
Define modality
The type of info. Eg touch, pressure, pain, temp etc
What is labelled line theory?
Modality is nerve specific not receptor specific
The brain knows pain vs touch because it has a map of what receptor is at the end of each nerve fibre, not because it can tell what receptor is at the end
Describe tonic vs phasic adaption and provide an example of each.
Tonic receptors turn on, and slowly adapt downwards. They fire the whole time the stimulus is on - eg pain
Phase receptors rapidly adapt, then have a smaller peak when stimulus turns off - eg putting on a tshirt.
Explain how lateral inhibition increases accuracy using an example.
If skin is poked by a pencil, multiple receptors are targeted, those closer to the point moreso than those further away.
Lateral inhibition means that the receptors further from the point are turned off, so only transmission from where the strongest stimulus is continues - i.e. where the point of the pencil is.
Explain how the patellar reflex assists with standing
The reflex stimulates the extensor muscle, and the spinal cord then inhibits the flexor muscle.
I.e. if the hamstrings aren’t inhibited, we wouldn’t be able to stand up.
What is the golgi organs function?
Measures the degree of tension on the tendon to prevent overstretching via the alpha motor neuron inhibiting the muscle if the stretch on the tendon is too strong
What is the clinical significance of the pupillary light reflex?
- allows testing for whether the occulomotor nerve, optic tract is is damaged
- Eg if right eye moves but left eye doesnt, then the occulomotor nerve on the left is where the issue is. Optic nerve is fine if message still gets to brain stem
What is the vestibulo-occular reflex?
- Keeps the eyes locked on a target whilst head rotates
- eye movement in comatose patient indicates brain stem still functioning
What is special about the fovea?
Any light that hits here gets fused into one image from both eyes and is area with higher visual accuity.
It has only cones.
Why do we have a blind spot?
From the spot where the optic nerve exits the eye
What is presbyopia?
When the cells in the lens that are further away from the fluid start to die off over a lifetime - requires glasses.
What is glaucoma?
When the canal of schlemm gets blocked with aqueous humor and pressure builds up.
Describe what happens in the eye for long-distance viewing.
- light doesnt have to bend as much
- sympathetic stimulation
- ciliary muscle is relaxed
- suspensory ligaments are taut
- lens is weak and flat
Describe what happens in the eye for short-distance viewing.
- parasympathetic stimulation
- light has to bend further
- ciliary muscle is contracted
- suspensory ligaments are slack
- lens is strong and round
What is accommodation referring to?
The change in the strength and shape of the lens
What is function of cones and rods?
Cones - colour vision. Have less discs so are less sensitive to light.
Rods - black and white vision. Have more discs so are more sensitive to light.
What is the macula lutea?
Area immediately around fovea.
Has fairly high accuity.
Describe path of sound from outer ear through to inner ear.
- sound wave enters outer ear
- tympanic membrane (ear drum) vibrates
- 3 bones in middle ear vibrate
- oval window vibrates
- wave enters cochlear
- low notes/long frequency will continue through cochlear for longer before hitting organ of corti
- high notes/short frequency will distort the endolymph earlier in the organ of corti
- round window vibrates
What is the role of the inner ear hair cells?
- hairs on basilar membrane are bent when the basilar membrane is deflected in relation to the stationary tectorial membrane
- bending of hair opens mechanically gated channels via TP links
- leads to ion movements and receptor potential
What is the role of the outer ear hair cells?
- receive efferent input
- move to amplify wave
- tunes and enhances response of inner hair cells
Describe the AP process in receptor hair cells (inner ear):
- TP links stretch and open channels
- stereocilia bend towards tallest member
- K+ enters (note: K is higher on outside for these cells as opposed to the usual of K+ higher inside)
- hair cell depolarises
- voltage gated Ca2+ channels open
- Ca enters and more neurotransmitter exits
- more AP in post-synaptic cell
